This study concerns effects of two main variables on hydrodynamics and mass transfer in the liquid-liquid two-phase slug flow regime. The influence of size of square and rectangular microchannels and presence of sodium dodecyl sulfate (SDS) are investigated. Three microchannels with dimensions 600×600 (MC600), 400×400 (MC400) and 600×300 (MC300) μm were used with hydraulic diameters of 600, 400 and 400 μm respectively. The results revealed that decreasing the hydraulic diameter improved the interfacial area due to slug length enlargement in both phases. Furthermore, mass transfer resistance was reduced because of enhanced internal circulations, leading to considerable enhancement of the overall mass transfer coefficient K_L. It was also found that the enhancement of K_L was greater in the square MC400 microchannel than in the rectangular MC300, as compared to the MC600. The enhancing benefit from internal circulations in organic slugs in rectangular microchannels decreased at higher aqueous flow rates due to enlarged stagnant liquid film flow between the organic slug and the microchannel wall. The presence of SDS slightly increased the interfacial area by reducing the slug length in both phases. However, there was a significant decrement in K_L, due to a greater mass transfer resistance.
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